1. Field Of The Invention
This invention relates generally to apparatus for making bottom hole shut-in pressure measurements in a well.
2. Description Of The Prior Art
The prior art includes a number of apparatus which provide means for shutting in a well at a desired downhole elevation, and then providing pressure communication across the shut-in point so that the measurement of pressure within the well below the shut-in point can be performed.
One example of such a tool is that shown in U.S. Pat. No. 4,134,452 to Kingelin. The Kingelin '452 tool includes a locking mandrel which is landed in a landing nipple located in the tubing string. A tool stem is run into the well on a wireline and is sealingly received within the bore of the locking mandrel. The tool stem includes a central opening which provides for pressure communication with a pressure indicating device.
Other somewhat similar devices are shown in U.S. Pat. No. 4,051,897, also to Kingelin and in U.S. Pat. No. 4,252,195 to Fredd.
The prior art also includes a prior commercial use by the assignee of the present invention of apparatus somewhat like that described above, for the purpose of shutting in an injection well and then measuring pressure fall-off data in the formation into which fluids have been injected. This prior use involved apparatus illustrated in FIGS. 2-5 of the present application.
FIG. 2 depicts a Model "FWG" bypass blanking plug with removable mandrel manufactured by Baker Packers, a division of Baker International Corporation of Houston, Tex. This Model "FWG" bypass blanking plug is disclosed at page 893 of Volume 1 of the 1982-1983 Composite Catalog of Oilfield Equipment and Services. The bypass blanking plug illustrated in FIG. 2 is constructed for use with a Model "F" seating nipple also manufactured by Baker Packers, as illustrated at page 888 of Volume 1 of the 1982-1983 Composite Catalog of Oilfield Equipment and Services.
The aforementioned prior use by the assignee of the present invention utilized a Baker Packers Model "FWG" bypass blanking plug which had been modified as shown in FIG. 3, and which was used in connection with a pressure communication mandrel illustrated in FIG. 4.
In FIG. 3, the Baker Packers Model "FWG" bypass blanking plug has had its sliding central mandrel and other related components removed, and has had an annular insert A inserted therein. The insert A has defined in the upper end thereof a conically tapered guide means B. The bottom clean-out plug C seen in FIG. 2 has been removed as part of the modifications illustrated in FIG. 3.
In this prior commercial use, the modified Baker Packers Model FWG bypass blanking plug of FIG. 3 was landed in a Baker Packers Model "F" seating nipple located above a subsurface formation into which fluid was being injected. Then, the pressure communication mandrel of FIG. 4 was assembled with a pressure measuring apparatus and lowered into engagement with the modified Baker Packers Model "FWG" bypass mandrel as illustrated in FIG. 5, so that further downward flow of fluid was stopped. The pressure measuring apparatus connected to the upper end of the pressure communication mandrel communicated through the pressure communication mandrel with the subsurface formation so as to measure pressure fall-off in the formation while isolating the formation from hydrostatic pressure within the well tubing.
The prior use described above involved small diameter 1.900-inch OD tubing. The Baker Packers Model "F" nipple had a 1.50-inch inner bore in which the Model FWG bypass blanking plug was landed.
The bypass blanking plug had a bore D of about 0.375 inches inside diameter in which the lower end of the pressure communication mandrel of FIG. 4 was received.
With this relatively small diameter equipment, it was possible to pull the pressure communication mandrel out of engagement with the Model "FWG" bypass blanking plug by pulling upwards on the pressure communication mandrel with a standard wireline. A pull of only approximately 400 to 500 pounds was required to disengage the pressure communication mandrel of FIG. 4 from the combined apparatus illustrated in FIG. 5. This necessary upward pressure is dependent upon the difference between the hydrostatic head trapped above the pressure communication mandrel and the lower pressure found in the well below the pressure communication mandrel, and is also dependent upon the cross-sectional area of the lower portion of the pressure communication mandrel.
While the approach taken in the prior art apparatus illustrated in FIGS. 2-5 wherein the Baker Packers Model "FWG" bypass blanking plug is modified by removing its mandrel and replacing it with a pressure communication mandrel like that of FIG. 4 is satisfactory for small diameter tubing like that described, such an approach is less satisfactory for larger sizes of equipment. In larger tubing the necessary diameter of the lower portion of the pressure communication mandrel in order to fill the plug body opening is so large that a very large upward force would be necessary to overcome the hydrostatic head trapped above the pressure communication mandrel. When the upward force necessary to disengage the pressure communication mandrel is greater than that which can be provided by a standard wireline apparatus, the use of this procedure becomes much less desirable.
Also the apparatus of FIGS. 2-5 is suitable only for use in an injection well. It is not suited to use in a producing well.